In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), studies are being actively carried out on the standardization of mobile communication standards in order to realize low-delay and high-speed transmission.
To realize low-delay and high-speed transmission, OFDM (Orthogonal Frequency Division Multiplexing) is adopted as a downlink (DL) multiple access scheme, while SC-FDMA (Single-Carrier Frequency Division Multiple Access) using DFT (Discrete Fourier Transform) precoding is adopted as an uplink (UL) multiple access scheme. SC-FDMA using DFT precoding forms an SC-FDMA signal (spectrum) by spreading and code-multiplexing a symbol sequence using a DFT matrix (precoding matrix or DFT sequence).
Furthermore, standardization of LTE-Advanced (or IMT (International Mobile Telecommunication)-Advanced) that realizes still higher speed communication than LTE has been started. LTE-Advanced is expected to introduce a radio communication base station apparatus (hereinafter referred to as “base station”) and a radio communication terminal apparatus (hereinafter referred to as “terminal”) capable of communicating at wideband frequencies to realize higher speed communication.
In order to maintain single carrier characteristics (e.g. low PAPR (Peak-to-Average Power Ratio) characteristics) of a transmission signal for realizing high coverage on an LTE uplink, allocation of frequency resources on the uplink is limited to allocation whereby an SC-FDMA signal is mapped in a localized manner to continuous frequency bands.
However, when allocation of frequency resources is limited as described above, vacant resources are produced in uplink shared frequency resources (e.g. PUSCH (Physical Uplink Shared CHannel)) and the efficiency of use of frequency resources in the system band deteriorates, resulting in deterioration of system throughput. Thus, clustered SC-FDMA (C-SC-FDMA) is proposed as a prior art for improving system throughput whereby an SC-FDMA signal is divided into a plurality of clusters and the plurality of clusters are mapped to discontinuous frequency resources (e.g. see Non-Patent Literature 1).
According to C-SC-FDMA, a base station compares the states of availability of frequency resources (subcarriers or resources blocks (RB)) of a plurality of uplinks or channel quality information (e.g. CQI: Channel Quality Indicator) between a plurality of terminals and the base station. The base station divides an SC-FDMA signal (spectrum) of each terminal by an arbitrary bandwidth according to the level of CQI between each terminal and the base station and thereby generates a plurality of clusters. The base station then allocates the plurality of clusters generated to frequency resources of a plurality of uplinks and reports information indicating the allocation results to the terminals. The terminal divides the SC-FDMA signal (spectrum) by an arbitrary bandwidth, maps the plurality of clusters to the frequency resources of the plurality of uplinks allocated by the base station and thereby generates a C-SC-FDMA signal. The base station applies frequency domain equalization (FDE) processing to the received C-SC-FDMA signal (a plurality of clusters) and combines the plurality of clusters after the equalization processing. The base station then applies IDFT (Inverse Discrete Fourier Transform) processing to the combined signal to obtain a time domain signal.
C-SC-FDMA maps a plurality of clusters to a plurality of discontinuous frequency resources, and can thereby perform frequency resource allocation among a plurality of terminals more flexibly than SC-FDMA. Thus, C-SC-FDMA can improve the multiuser diversity effect and can improve the system throughput in consequence (e.g. see Non-Patent Literature 2).